North Carolina's Strategic Prioritization process has made the state a national leader in data-driven infrastructure investment. A critical component of this process is the estimation of travel time savings, used in the benefit-cost ratio for scoring and selecting statewide mobility and regional impact projects. However, as each review cycle evaluates thousands of candidate projects, there is growing concern that the current additive approach, evaluating projects independently with fixed demand, fails to capture key network-level dynamics and interactions.
This research addresses five core limitations in current travel-time estimate modeling: (1) overlapping impacts from multiple projects, (2) induced demand and Braess paradox behavior, (3) corridor-level constraints that are not systematically enforced, (4) ambiguity in valuing equal vehicle-minute savings, and (5) sensitivity to project timing and non-unique select link estimates. These issues increase the risk of benefit misestimation and hinder the ability to identify project combinations that maximize system performance.
The goal of this project is to improve the accuracy, fairness, and transparency of travel time benefit estimation in North Carolina's Strategic Prioritization process by accounting for network-level interactions among transportation projects. The objectives are threefold:
- Quantify the impact of joint implementation effects on travel time savings estimates by simulating multiple project combinations using North Carolina Statewide Transportation Model (NCSTM) and identify conditions where interaction effects significantly alter benefit estimates or project rankings.
- Develop and deliver practical implementation tools, including a spreadsheet-based screening module, TransCAD GISDK scripts, and scoring comparison tables, to support integration of joint-effect modeling into current evaluations with minimal disruption to current workflows.
- Demonstrate policy-ready use cases through corridor-level pilot studies, illustrating how accounting for project interactions can improve prioritization decisions, support transparent justification of rankings, and identify opportunities for coordinated programming that maximizes systemwide benefits.
This research offers a practical, model-driven solution grounded in advances in network design optimization. The project's approach enables the Strategic Prioritization Office of Transportation (SPOT) Workgroup to identify when multiple projects should be evaluated together, and how scoring outcomes change when network interactions are taken into account. The project will produce usable tools, including GISDK scripts for NCSTM, a spreadsheet-based pre-evaluation screening tool, technical guidance, and ranking comparison tables, to inform when, where, and how to apply these insights within the existing prioritization process.
This research is both timely and aligned with STI law's mandate for continuous improvement. It offers a clear path to enhancing the realism, fairness, and defensibility of travel time benefit estimation while respecting SPOT's operational constraints. Most importantly, it will help ensure that public funds are directed to the highest and best use, by identifying project combinations that truly improve access, reliability, and system performance. The project is designed to support near-term implementation and scale with future STIP cycles.
